Design and demonstration of a high temperature solar-heated rotary tube reactor for continuous particles calcination

This study aims at developing a novel solar reactor concept for the continuous processing of reactive particles involved in high-temperature thermochemical reactions (500–1600 °C). The reactor is composed of a cavity-type solar receiver for radiation absorption and heat transfer to a rotary tube in which the reactive particles are continuously injected. This type of reactor shows several advantages in comparison with existing solar thermochemical reactors and the main key characteristics are: (i) external heating by concentrated solar energy, (ii) indirect heating of reactants (reacting zone separated from the zone receiving solar radiation) thus avoiding products deposition on the optical window, (iii) continuous injection of solid reactive particles, (iv) rotation of the tube enabling particles transport and circulation to the outlet, (v) uniform heating of the reactive zone, (vi) direct contact between particles and inner tube wall, enabling optimal heat transfer, (vii) long residence time of particles controlled by the adjustable tube tilting angle, tube rotational speed and particle feeding rate, (viii) reactor adapted to various solid-gas reactions and possible large-scale extrapolation. This versatile solar reactor can be operated for a large variety of thermochemical processes involving solid reactants such as calcination reactions (e.g. decarbonation of limestone for lime or cement production). In this study, proof-of-concept experiments were performed to demonstrate the feasibility of continuous solar calcination of limestone particles (CaCO3 → CaO + CO2(g)), which for example could be associated to a cement production solar process, but also applied to CaO-based sorbent regeneration in a CO2 capture process or thermochemical energy storage via CaCO3/CaO reversible reactions.